Many expensive electronic components are packaged in trays, in which multiple discrete components are arranged in a matrix on each tray. The trays are designed so that multiple trays can be stacked together to increase the number of components positioned in one place, such as for transport or on a pick-and-place board assembly machine. During transport, each stack of trays is tied together with strapping material and packaged inside Electro-Static Discharge (ESD) bags. Typically, each stack of tray carries components of the same part number and lot code, with the part number and lot code information printed on a label attached to the outside of the bag. No identification of the components is generally available inside the bag, nor is such identification printed on the tray. If the trays are removed from such bags, the user must carefully preserve the identity of the components in the trays.
Electrical components are usually placed onto printed circuit boards by a component placement machine. The most common configuration for components provided on trays is a tray tower on the placement machine. Trays of different part numbers are placed onto different ‘movable’ drawers inside the tray tower. At least one tray of components can be placed into each drawer. Sometimes, a stack of trays can be placed onto one drawer and the placement machine can remove the tray on the top of the stack after all the components on the top tray are consumed. The placement machine selects different part numbers by moving the entire drawer assembly up and down, or otherwise positioning the pick head with respect to a desired drawer. The drawer with the desired part number is then pulled out from the tray tower for picking. In many machines, the dispensing of the components is always at the same level since the pick up mechanism of the placement machine is configured to always pick up components at the same vertical position.
Many component verification systems require the operator to scan a part number barcode label on the bag in which the components are delivered. Then the operator scans the drawer number and the software verifies if the part number and the drawer number are a correct match. This approach is dependent on the operator scanning the correct part number and drawer number, and in many situations, trays from different bags are mixed into a single stack of trays. Some have suggested placing unique barcode labels to the bottom of each drawer, and scanning the barcode when the drawer is pulled out from the tower. Barcode scanning has also been employed to verify proper configuration of component reels and corresponding slots on placement machines. Other approaches to component identification and verification have also been considered or may be in use.